In integrated semiconductor circuits, the degree of integration has increased recently and LSIs and VLSIs have been put to practical use. With these trends, the minimum pattern line width in such integrated circuits has reached a sub-half-micron region and is decreasing further.
Because of the above, the photolithographic requirements for forming fine patterns are increasingly becoming severer. Known as one means for attaining finer patterns is to use an exposure light having a shorter wavelength in resist pattern formation.
For example, the i-ray (365 nm) emitted from a high-pressure mercury lamp has been used so far in the production of DRAMs having degrees of integration of up to 64 megabits. In processes for mass-producing 256-megabit DRAMs, KrF excimer laser light (248 nm) has come to be practically used as an exposure light substitute for i-ray. For use in producing DRAMs having a degree of integration of 1 gigabit or higher, exposure lights having even shorter wavelengths are being investigated and use of ArF excimer laser light (193 nm), F.sub.2 excimer laser light (157 nm), X-rays, and electron beams is thought to be effective [see Takumi Ueno et al., "Tan-hacho Fotorejisuto Zairyo-ULSI Ni Muketa Bisaikako-(Short-wavelength Photoresist Materials--Fine Processing toward ULSIs-)", Bunshin Shuppan, 1988].
In particular, exposure with an ArF excimer laser is regarded as a next-generation exposure technique. There is hence a desire for the development of a resist which has high sensitivity, high resolution, and excellent dry-etching resistance and is suitable for exposure with an ArF excimer laser.
Conventional resist material sin extensive use for exposure to i-ray and KrF excimer laser light include resists which contain an aromatic polymer so as to obtain high resistance to dry etching. For example, novolak resists and chemical amplification type polyvinylphenol resists are known. However, due to the aromatic rings, which have been incorporated for the purpose of imparting dry-etching resistance, such resists transmit substantially no light in the wavelength range for ArF excimer laser light. Those conventional resists hence have a drawback in that it is difficult to irradiate a bottom layer of the resist film with the light, so that a pattern having satisfactory sectional shapes cannot be obtained.
A technique known as one measure for eliminating the problem concerning resist transparency is to use an aliphatic polymer containing no aromatic rings, e.g., poly(methyl methacrylate) (see J. Vac. Sci. Technol., B9, 3357 (1991)). However, such a polymer is not expected to have sufficient dry-etching resistance and is hence incapable of practical use. Consequently, the most important subject in developing a resist material for exposure with an ArF excimer laser is to attain both improved transparency and high resistance to dry etching.
Under these circumstances, it has been reported in Proc. SPIE, 1672, 66 (1992) that a resist containing alicyclic hydrocarbon groups in place of aromatic rings is equal in dry-etching resistance to resists containing aromatic rings and shows reduced absorption at 193 nm. This report has led to recent enthusiastic investigations on the utilization of that kind of polymer.
Attempts have been made from long ago to apply a polymer having alicyclic hydrocarbon groups to resists. For example, JP-A-60-195542 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-1-217453, and JP-A-2-59751 disclose norbornene polymers, and JP-A-2-146045 discloses various alkali-soluble resins having alicyclic hydrocarbon skeletons and maleic anhydride units.
JP-A-5-80515 discloses a copolymer of norbornene and an acrylic ester protected with an acid-decomposable group. JP-A-4-39665, JP-A-5-265212, JP-A-5-80515, and JP-A-7-234511 disclose copolymers having adamantane skeletons in side chains. JP-A-7-252324 and JP-A-9-221526 disclose polymeric compounds in which alicyclic hydrocarbon groups having 7 to 12 carbon atoms comprising a crosslinked cyclic hydrocarbon group have been bonded to side chains thereof; examples of such alicyclic hydrocarbon groups include tricyclo[5.2.1.02.6]decanedimethylene, tricyclo[5.2.1.02.6]decanediyl, norbornanediyl, norbornanedimethyl, and adamantanediyl groups. JP-A-7-199467 discloses a polymeric compound having tricyclodecanyl, dicyclopentenyl, dicyclopentenyloxyethyl, norbornyl, or cyclohexyl groups bonded to side chains thereof.
FP-A-9-325498 discloses a polymer having a main chain containing cyclohexane and isobornyl skeletons. JP-A-9-230595, JP-A-9-244247, JP-A-10-10739, WO 97-33198, EP 794458, and EP 789378 disclose polymers having a main chain containing any of various cycloolefins, e.g., dicycloolefins, incorporated therein. JP-A-8-82925 and JP-A-9-230597 disclose a preference for compounds having a terpenoid skeleton having a menthyl group or menthyl derivative group.
There also is a technique of adding a low-molecular dissolution inhibitor to thereby heighten resolution. JP-A-8-15865 discloses use of a t-butyl ester of androstane as a dissolution inhibitor, while JP-A-9-265177 discloses a low-molecular dissolution inhibitor comprising a norbornyl, adamantyl, decanyl, or cyclohexyl group and an acid-decomposable group bonded thereto. It has been reported in Proc. SPIE, 3049, 84 (1997) that use of an oligomer of t-butyl lithocholate as a dissolution inhibitor is effective in improving adhesion and contrast.
The conventional, chemical amplification type positive resists containing an aromatic polymer which are for use with a KrF excimer laser have a problem as reported, e.g., in Prooc. SPIE, 1672, 46 (1992), Prooc. SPIE, 2438, 551 (1995), Prooc. SPIE, 2438, 563 (1995), Prooc. SPIE, 1925 14 (1993), J. Photopolym. Sci. Tech., Vol.8, No.4, 535 (1995), J. Photopolym. Sci. Tech., Vol.5, No.1, 207 (1992), J. Photopolym. Sci. Tech., Vol.8, No.4, 561 (1995), and Jpn. J. Appl. Phys., 33, 7023 (1994). The problem is that as the standing period of from exposure to heat treatment (PEB) becomes longer, the acid which has generated diffuses or the acid present on the resist surface is deactivated by basic impurities present in the atmosphere. As a result, the resist has impaired sensitivity and gives, through development, resist patterns which are not uniform in profile and line width.
A known technique for eliminating the above problem is to add an amine to a chemical amplification type resist containing an aromatic polymer. This technique is disclosed in many documents including JP-A-63-149640, JP-A-5-249662, JP-A-5-127369, JP-A-5-289322, JP-A-5-249683, JP-A-5-289340, JP-A-5-232706, JP-A-5-257282, JP-A-6-242605, JP-A-6-242606, JP-A-6-266100, JP-A-6-266220, JP-A-6-317902, JP-A-7-120929, JP-A-7-146558, JP-A-7-319163, JP-A-7-508840, JP-A-7-333844, JP-A-7-219217, JP-A-7-92678, JP-A-7-28247, JP-A-8-22120, JP-A-8-110638, JP-A-8-123030, JP-A-9-274313, JP-A-9-166871, JP-A-9-292708, JP-A-9-325496, JP-A(PCT)-7-508840 (the term "JP-A(PCT)" as used herein means an "unexamined published Japanese patent application in PCT"), and U.S. Pat. Nos. 5,525,453, 5,629,134, and 5,667,938.
When any of the amines the use of which is disclosed in the above references is added to a chemical amplification type resist for exposure to ArF excimer laser light which contains a nonaromatic polymer having a main chain structure comprising alicyclic hydrocarbon units, then this addition is effective in diminishing the change in sensitivity and in obtaining, through development, resist patterns more uniform in profile and line width, as in the case of resists containing an aromatic polymer. However, the addition of those amines to such resists containing an alicyclic polymer results in exceedingly poor performance with respect to image defects. An effective measure for this has been desired.